Field of the Invention
The present invention relates to a radiation imaging system.
Description of the Related Art
A radiation imaging apparatus includes a panel in which a plurality of pixels for detecting radiation are arranged, and a readout circuit for reading out signals from the panel. Each pixel can include a converter for converting radiation into an electric signal, and a transistor connected to the converter. If the radiation imaging apparatus is irradiated with radiation through a subject, signals corresponding to the emitted radiation are accumulated in the converters, and the readout circuit reads out, via the transistor, signals corresponding to the accumulated signals. This obtains a radiation image. In a state in which the radiation imaging apparatus is not irradiated with radiation, noise components can be accumulated in the converters. An image corresponding to the noise components can be read out as an offset image.
The radiation imaging apparatus can obtain an image from which the noise components are removed, by calculating the difference between the radiation image obtained by detecting the irradiated radiation and the offset image obtained in the state in which the radiation imaging apparatus is not irradiated with radiation. However, if the state of the radiation imaging apparatus when obtaining the radiation image is different from the state of the radiation imaging apparatus when obtaining the offset image, it is impossible to correctly remove the noise components from the radiation image. Japanese Patent Laid-Open No. 2011-101693 describes a radiation image forming apparatus which has an imaging enable state and a sleep state, and causes a readout IC to perform a readout operation by supplying power to the readout IC in the sleep state or when transiting from the sleep state to the imaging enable state.
As described above, each pixel of the radiation imaging apparatus includes the converter and the transistor connected to the converter. If an OFF voltage (a voltage for turning off the transistor) is applied to the gate of the transistor of the pixel for a long time, a threshold may shift. If the threshold of the transistor of each pixel shifts, the influence of the shift appears in a radiation image as fixed pattern noise.